Two versions of Redsn0w are being developed right now for iOS 4.2.1 jailbreak. Redsn0w 0.9.6 builds can jailbreak iOS 4.2.1 (tethered only) on all devices whereas Redsn0w 0.9.7 builds bring untethered jailbreak support for iOS 4.2.1 on newer devices only i.e., iPhone 4, iPod Touch 4G and iPad.

The necessary requirement for untethered jailbreak is that you have SHSH blobs for iOS 4.2 b3 saved on Cydia servers. So, if you didn’t save SHSH blobs or you have got one of old devices like iPhone 3G(S), iPod Touch 3G, you can use Redsn0w 0.9.6 rc7 to jailbreak the device and perform one-click tethered boot.

One Click tethered boot feature in Redsn0w 0.9.6RC7 allows you to skip almost all steps and you can get booted your device with single command or one click.

Step 2: Place Redsn0w.exe and iOS 4.2.1 IPSW file in one top-level folder just for convenience; as you can see I have placed these two files in the folder “jailbreak” on E drive.

Step 3: If you are a Windows 7/vista user, make it sure that you run Redsn0w in compatibility mode. For this purpose right-click on Redsn0w.exe file and click on “Properties”. Go to “Compatibility” tab and check these two options:

If you don’t know how to use command prompt or you don’t want to type those commands on every boot, you can also create a short-cut file for this purpose.

To ease the procedure we will use the shortcut file “boot-ipt4g” which you find in the redsn0w folder downloaded in Step 1. Right click on it to open the properties.

Go to “Shortcut” tab and type the exact path of Redsn0w.exe and respective iOS 4.2.1 file in the field of “Target”. As we have already placed these two files in E:\jailbreak folder, so we will use this:

Place type the correct file names and destination folders if you have changed the files names or placed these files in any other location.

Now go to “Compatibility” tab to run Redsn0w in compatibility mode. See the Step 3 for more details. You can also go to “General” tab and change the file name from “boot-ipt4g” to any name like “boot-iphone3gs” etc.

Apply the changes and save the file. Now double-click on this shortcut file to run the redsn0w without typing any commands.

For Mac Users:

To get the one-click tethered boot on Mac, type the following command, assuming that all the files are on desktop: